The invention relates to a motor vehicle seat with integrated occupation detector.
To protect the front-seat passenger in a vehicle in the event of an accident, an increasing number of motor vehicles are being equipped with a front-seat passenger airbag. To prevent unnecessary damage when this airbag is tripped, it should be tripped in an accident only if the front passenger seat is occupied.
Meanwhile a number of systems for detecting occupation of vehicle seats are known. For example, motor vehicle seats with a pressure-sensitive sensor mat integrated in the upholstery are known. To ensure satisfactory operation of these systems, these sensor mats must be taken into account in the design of the seat upholstery. In practice this may lead to difficulties, because the designer of the seat upholstery is confronted with new requirements, which additionally restrict his creative freedom.
There are likewise systems for detecting occupation of motor vehicle seats in which sensors are not installed in the seat upholstery. These are, for example, infra-red or ultrasonic sensors or inductive or capacitive sensors, all of which are mounted in the motor vehicle itself. However, these systems are regarded as more susceptible to faults than the systems directly integrated in the motor vehicle seat. In addition these systems are far more expensive than the pressure-sensitive systems.
The European patent application EP-A-0 670 239 describes a vehicle seat with occupation detector, in which an upper frame in the front area of the seat is tiltable on a lower frame of the seat. A leaf spring, which lifts the rear area of the upper frame when the seat is not occupied and is elastically deformed under the weight of the occupant, is arranged between the upper frame and lower frame of the seat. The displacement of the upper frame of the seat resulting from the deformation of the leaf spring is recorded by a measuring sensor and seat occupation thus concluded.
The document WO-A-98/25112 (D2) also describes a vehicle seat with an occupation detector. In this vehicle seat the upper frame lies flat at several points on the lower frame and is bolted to the latter. A force measuring sensor, which can measure the bearing force of the upper frame on the lower frame, is arranged between the upper frame and lower frame at each of the bolted connection points.
The task of the invention is to propose a motor vehicle seat with an alternative simple, cheap and reliable occupation detector, in which the design of the seat upholstery is not affected by the occupation detector.
According to the invention this problem is solved by a motor vehicle seat according to claim 1. Like most modern vehicle seats, a seat of this type comprises an upper frame, which supports seat upholstery or a seat shell, and a lower frame, which is secured in the motor vehicle, as well as mechanical mounting elements for supporting the upper frame in the lower frame and for introduction of a weight force from the upper frame into the lower frame. According to the invention these mounting elements are designed in such a way that they deform elastically, i.e. reversibly, under the weight of a seat user, the occupation detector still comprising at least one measuring sensor, which measures this elastic deformation directly or indirectly. In other words the mounting elements, which support the upper frame in the lower frame, are used as converters, which convert the weight of the seat user into a geometric variable measurable by a simple measuring sensor. These mounting elements thus permit a simple, reliable and low-cost occupation detector without the need to install a sensor in the seat upholstery. Furthermore, it should be noted that such a detector can be integrated easily in the seat and is extremely rugged. As wide scope exists for selection of the measuring sensor, the latter can be selected with consideration of specific requirements, which relate, for example, to the reliability, the temperature range or the electromagnetic compatibility. The cost of the measuring sensor and the electronic evaluator to be connected to it in series will certainly likewise play a role in the selection of the measuring sensor.
The measuring sensor may, for example, be a strain gauge, which is mounted on the mounting element in such a way that it directly measures its deformation (e.g. bending or torsion). However, the mounting elements are preferably designed in such a way that their elastic deformation causes vertical displacement between the upper frame and lower frame. Consequently the measuring sensor can be a displacement sensor, which measures this relative displacement in the vertical direction. As the amplitude of the displacement to be measured can easily be adapted in an optimum manner to the measuring range of a selected displacement sensor via the deformability of the mounting elements, extremely simple, inexpensive displacement sensors can be used. In the simplest case the displacement sensor may even be a simple switching element, which measures a relative vertical displacement between the upper frame and lower frame caused by the deformation of the mounting elements as the exceeding of a threshold value. If the switching element comprises several switching points, to which a predetermined threshold value is assigned, the vehicle occupant can even be classified in a specific weight category. This permits weight-dependent control of the airbag in the simplest way. A similar result can, of course, also be achieved by several switching elements, a predetermined threshold being assigned to each switching element.
The elastically deformable mounting element, which is realised in a motor vehicle seat according to the invention, may have many different embodiments. For example, it may be designed as a simple bolt, which is secured unsupported to one of the two frames and forms a support for the other frame. The bending of the bolt is then measured by the measuring sensor. However, a bolt of this type would have to be a certain length, so that a change in the dead weight on the seat can also be measured by simple measuring sensors. Multi-part mounting elements, in which separate spring elements (e.g. spring washers, leaf springs or spiral springs) are used, are also conceivable.
In a preferred embodiment the mounting element is designed as a stirrup with a first and second arm, the free end of the first arm being securely connected to one of the two frames and the free end of the second arm forming a support for the other frame. This stirrup is then designed in such a way that the opening width of the stirrup changes elastically under the weight of a seat user. (An additional weight preferably produces reduction of the opening width of the stirrup). In the area of the support the first stirrup arm is advantageously separated from the second stirrup arm by a gap. The opening width of this gap is preferably designed in such a way that the support rests on the first stirrup arm before plastic deformation of the stirrup takes place, so that the risk of continuous impairment of the function of the stirrup by overloading is clearly reduced.
In an advantageous embodiment of the stirrup the first and second stirrup arms are designed in such a way that they exhibit approximately the same bending deformation with vertical loading of the support. Consequently it is ensured that the support is displaced largely parallel with itself under the weight of a seat user (or in other words: the rotation on the support caused by the bending deformation is negligible). Consequently the risk of tilting of the parts movable in relation to each other is avoided.
An easily manufactured mounting element for the motor vehicle seat according to the invention comprises a shaft, which is clamped securely to one of the two frames, and a head arranged as an axial extension of the shaft, which forms a first shoulder area. A gap extends from this first shoulder area into the head. Consequently an unsupported arm, which forms at its free end a support for the other frame, is formed at the head, the opening width of the gap changing elastically under the weight of a seat user. A stirrup, the first arm of which is formed by the shaft and the connected part of the head and its second arm by the unsupported arm, is thus formed. The head advantageously has a quite large horizontal transverse hole, into which the gap terminates. This transverse hole is arranged and designed in such a way that a flexible stirrup element connecting the unsupported arm to a first arm, which is in turn rigidly connected to the shaft, is formed at the head end. However, the head may also have horizontal oblong holes, the gap terminating in one of these oblong holes. These oblong holes may advantageously be arranged in the head in such a way that the support is displaced largely parallel with itself in the vertical direction under the weight of a seat user.
With regard to the described mounting element it should be noted that its design can be particularly compact, if the head is offset in relation to the shaft,
In an alternative embodiment the mounting element comprises a journal and a journal bearing. The journal is securely connected to one of the two frames and the journal bearing to the other frame. A spring device designed in such a way that the journal is vertically displaced elastically in relation to the journal bearing under the weight of a seat user, is arranged between the journal and the journal bearing. The journal bearing advantageously has a vertical guide slot for the journal. Horizontal forces are transmitted between the two frames in this guide slot without horizontal displacement of the two frames.